The invention relates to a ring-gap nozzle for distributing a fluid medium over a bottom plate, comprising an axial channel passing through the plate, the said channel being covered by a cap so as to leave a ring gap between the cap and the plate, while the cap is held by means of a connecting member which passes coaxially through the channel and is attached to a clamp which is mounted at the start of the channel, in the direction of a flow of the medium, thus forming an annular flow space in which the medium flowing in the channel region axially is deflected in a deflection space and flows out radially through the ring gap, all walls bounding the flow space being constructed in such a way that the cross section of the flooded area of the ring-shaped flow space continuously decreases in the direction of flow of the medium towards the outlet edge of the ring gap, beginning at least in the deflection space of the flow space.
Ring-gap nozzles of this kind are described for instance in U.S. Pat. No. 4,371,115 and often used in fluidized bed dryers serving there to distribute the medium which holds the granular product in the bed of the dryer fluidized. The special design of the ring-gap nozzles allows the inflowing medium to be conducted to the plate of the fluidized bed dryer in such a way as to prevent the product to be treated from settling on the bottom plate of said fluidized bed dryer as well as to prevent settling of particles entrained by the medium in the channel and in the deflection space of the nozzle.
The disadvantage of the ring-gap nozzles known hitherto, however, is that the product present in the fluidized bed dryer may flow back into the nozzles when the flow of medium is cut off. As the maximum deflection of the medium flow in this type of ring-gap nozzle is 90.degree. or even a bit less, the medium does not coat the bottom plate of the dryer in the proximity of the nozzle in an ideal manner, thus the effect is reduced. Should it be necessary to close the ring-gap nozzles known hitherto, it should demand complicated manipulation. Furthermore, the ring-gap nozzles known thus far are neither easy nor inexpensive to manufacture.